Methane sensor automatic baseline calibration

ABSTRACT

A method for baseline calibration of methane sensor includes receiving data characterizing methane detection by a sensor and sensor measurement parameters. The received data characterizing methane detection includes a plurality of methane measurements and detection times associated with the plurality of methane measurements. The method also includes determining a first plurality of calibrated methane measurements by at least calibrating the plurality of methane measurement based on the sensor measurement parameters and one or more of a humidity and a temperature associated with the sensor. The method further includes calculating an offset parameter based on a difference between a global baseline reference and one of a previous baseline value and a measurement baseline value associated with the first plurality of calibrated methane measurements. The method also includes providing a second plurality of calibrated methane measurements by at least subtracting the offset parameter from the first plurality of calibrated methane measurements.

BACKGROUND

Sensors can be deployed in a variety of environments for sensingcontaminants and concentration of particles that need to be tracked inthe environment. Some sensors (e.g., methane sensor) can be placedaround gas well pads to detect gas (e.g., methane) leaks. Datacorresponding to detection by the sensor can be transmitted to acontroller that can process the data, determine the concentration ofcontamination and generate notification if the concentration of thecontamination exceeds desired levels.

SUMMARY

Various aspects of the disclosed subject matter may provide one or moreof the following capabilities.

In one implementation, a method for baseline calibration of methanesensor includes receiving data characterizing methane detection by asensor and sensor measurement parameters. The received datacharacterizing methane detection includes a plurality of methanemeasurements and detection times associated with the plurality ofmethane measurements. The method also includes determining a firstplurality of calibrated methane measurements by at least calibrating theplurality of methane measurement based on the sensor measurementparameters and one or more of a humidity and a temperature associatedwith the sensor. The method further includes calculating an offsetparameter based on a difference between a global baseline reference andone of a previous baseline value and a measurement baseline valueassociated with the first plurality of calibrated methane measurements.The method also includes providing a second plurality of calibratedmethane measurements by at least subtracting the offset parameter fromthe first plurality of calibrated methane measurements.

One or more of the following features can be included in any feasiblecombination.

In one implementation, the method further includes determining themeasurement baseline value. The determining includes selecting a subsetof methane measurements from the first plurality of calibrated methanemeasurements. The values of the subset of methane measurements are belowa predetermined percentile value and the measurement baseline value is amean of the subset of methane measurements.

In one implementation, determining the offset parameter includesdetermining that the measurement baseline value is less than a thresholdbaseline value; and determining the offset parameter based on differencebetween the measurement baseline value and the global baselinereference. In another implementation, determining the offset parameterincludes determining that the measurement baseline value is above athreshold baseline value; and determining the offset parameter based ondifference between the previous baseline value and the global baselinereference. The sensor measurement parameters, the global baselinereference, the threshold baseline value and the previous baseline valueare received from a database. In yet another implementation, the methodfurther includes updating the previous baseline value in the database,the updating including setting the previous baseline value to themeasurement baseline value.

Non-transitory computer program products (i.e., physically embodiedcomputer program products) are also described that store instructions,which when executed by one or more data processors of one or morecomputing systems, causes at least one data processor to performoperations herein. Similarly, computer systems are also described thatmay include one or more data processors and memory coupled to the one ormore data processors. The memory may temporarily or permanently storeinstructions that cause at least one processor to perform one or more ofthe operations described herein. In addition, methods can be implementedby one or more data processors either within a single computing systemor distributed among two or more computing systems. Such computingsystems can be connected and can exchange data and/or commands or otherinstructions or the like via one or more connections, including aconnection over a network (e.g. the Internet, a wireless wide areanetwork, a local area network, a wide area network, a wired network, orthe like), via a direct connection between one or more of the multiplecomputing systems, etc.

These and other capabilities of the disclosed subject matter will bemore fully understood after a review of the following figures, detaileddescription, and claims.

BRIEF DESCRIPTION OF THE FIGURES

These and other features will be more readily understood from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a flowchart of an exemplary method for calibrating amethane sensor;

FIG. 2 illustrates an exemplary industrial site where methane leaks orfugitive methane can be inspected by a methane sensor; and

FIG. 3 illustrates exemplary plots of calibrated methane measurements.

DETAILED DESCRIPTION

The operation of a methane sensor (e.g., a metal-oxide methane sensor)configured to detect methane leaks or fugitive methane at industrialsites can be impacted by the environment of the methane sensor. Forexample, temperature and/or humidity of the industrial site can affectthe methane measurement data generated by the methane sensor. Methanemeasurement data can be calibrated to account for changes in temperatureand/or humidity of the industrial site. However, the aforementionedcalibration may not compensate other variations in the methanemeasurement data (e.g., caused due to aging of the methane detector).These variations my lead to a drift in the baseline of the methanemeasurement by the methane detector (e.g., indicative of ambient methanelevels in the atmosphere). Some implementations of the current subjectmatter provides for automatically calibrating the drift in the measuredbaseline of the methane sensor. This can be done by using the averageglobal methane concentration in the atmosphere (e.g., 1.88 parts permillion by volume, or PPMv) or a site specific known ambient methaneconcentration as a reference (sometimes referred to as “global baselinereference”), and calibrating the measurement data based on the offsetbetween the measured baseline of the sensor and the global baselinereference of methane concentration.

FIG. 1 illustrates a flowchart of an exemplary method for calibrating amethane sensor. At step 102, data characterizing methane detection by asensor and sensor calibration parameters is received. The received datacharacterizing methane detection includes a plurality of methanemeasurements and detection times associated with the plurality ofmethane measurements. For example, the plurality of methane measurementscan include a methane measurement at each detection time. FIG. 2illustrates an exemplary industrial site 200 that can be inspected by amethane sensor for a methane leak or fugitive methane monitoring. Theindustrial site 200 can include a detection system 202 that can includeone or more sensors (e.g., methane sensor, temperature sensor, humiditysensor, etc.). The methane sensor in the detection system (not shown)can detect surrounding methane level (e.g., due to a methane leak in theindustrial site).

Data characterizing the methane detection can be transmitted (e.g.,periodically). For example, the methane sensor can be configured toactivate periodically (e.g., once a few minutes, once an hour, once aday etc.) and perform methane detection over a detection time-period(e.g., a predetermined period). After each detection time-period (or aset of detection time periods), data characterizing methane detectioncan be transmitted that can be received by the controller 204. Thecontroller 204 can also receive temperature and/or humidity measurementsfrom the industrial site 200 (e.g., by temperature and/or humiditydetector in the detection system 202).

The controller 204 can receive measurement parameters associated withthe methane sensor in the detection system 202 that can allow forcalibrating/calculating methane measurement data for varioustemperature, humidity and methane levels in the industrial site 200. Itcan be desirable to calibrate the measurement data from a methane sensorbecause the operation of the methane sensor can change based onenvironmental conditions. In some implementations, the measurementparameters can be stored in a database 206. Additionally or alternately,the measurement parameters can be provided by the methane sensor in theindustrial site 200.

Returning to FIG. 1 , at step 104, a first plurality of calibratedmethane measurements can be determined by calibrating the methanemeasurement data from the methane sensor (e.g., methane sensor indetection system 202). The measurement parameters along with temperatureand/or humidity measurements (e.g., by temperature/humidity sensors inthe detection system 202) can be used to generate calibrated methanemeasurements (“first calibration”). In some implementations, themeasurement parameters can be coefficients of a polynomial equation thatcan take temperature and/or humidity measurements values as inputs andgenerate a scaling factor based on which the methane measurement datafrom the methane sensor can be calibrated. As described above,calibrating the methane measurement data for temperature/humidity at theindustrial may not be sufficient. For example, additional calibrationmay be needed to account for drift in the baseline methane measurementby the methane sensor (e.g., due to aging of the methane sensor).

The additional calibration (“second calibration”) can be performed bydetermining a measurement baseline value associated with the calibratedmethane measurements (e.g., generated after temperature and/or humiditycalibration). Measurement baseline value can be determined by selectinga subset of the calibrated methane measurements. The subset ofcalibrated methane measurements can be determined by selecting a portionof the calibrated methane measurement that corresponds to apredetermined percentile value of the plurality of calibrated methanemeasurement (e.g., 20^(th) percentile, 25^(th) percentile, etc.). Inother words, the calibrated methane measurement that constitute apredetermined percentile range of the calibrated methane measurement(e.g., bottom quartile, bottom quintile, etc.) are selected in thesubset.

After the selection of the subset of calibrated methane measurements,the measurement baseline value can be a metric representative of thesubset (e.g., mean/median of the subset of calibrated methanemeasurements). The measurement baseline value can be representative ofatmospheric methane measurement by the methane sensor (e.g., after themethane leak at the industrial site 200 has dissipated and the methanesensor is detecting the atmospheric methane levels). It can be desirablethat the measurement baseline value matches the average global methaneconcentration in the atmosphere or a known site-specific ambient methanelevel (global baseline reference). The value of the global baselinereference can be around 1.88 PPMv. A discrepancy between the measurementbaseline value and the global baseline reference can indicate thatfurther calibration of the methane sensor is needed.

In some implementations, the measurement baseline value can be greaterthan a threshold baseline value (e.g., 5 parts per million of methane byvolume). This can be indicative of a persistent leak at the industrialsite 200. In other words, the methane sensor is unable to detect theatmospheric methane without the influence of the methane leak at theindustrial site 200. As a result, the measurement baseline value may notbe indicative of atmospheric methane measurement or global baselinereference, and the measurement baseline value of a previous measurementof the methane sensor (“previous baseline value”) may be a betterindicator of the atmospheric methane measurement by the sensor. Thethreshold baseline value can be stored in a database 206 and can bereceived by the controller 204.

At step 106, an offset parameter for the second calibration can becalculated. In some implementations, the offset parameter can be thedifference between the measurement baseline value and the globalbaseline reference (e.g., when the measurement baseline value is belowthe threshold baseline value). In some implementations, the offsetparameters can be the difference between the previous baseline value andthe global baseline reference (e.g., when the measurement baseline valueis above the threshold baseline value).

At step 108, a second plurality of calibrated methane measurements canbe provided (e.g., to the database 206, to a user via a graphical userinterface (GUI) display device. This can be done by determining thesecond plurality of calibrated methane measurements subtracting theoffset parameter from the calibrated methane measurement obtained fromthe first calibration. FIG. 3 illustrates exemplary plots of calibratedmethane measurements (in parts per million by volume [PPMv] vs detectiontimes [in minutes]). Plot 302 is the plot of the first plurality ofcalibrated methane measurements obtained after the first calibration(e.g., calibrating for temperature/humidity variations at the methanesensor). Plot 304 is the plot of the second plurality of calibratedmethane measurement obtained after the second calibration (e.g.,calibrating for deviations in measurement baseline value from globalbaseline reference by subtracting the offset value from the firstplurality of calibrated methane measurement). Marker 312 indicates thepredetermined threshold baseline value (e.g. 5 PPMv) and marker 314indicates the measurement baseline value (e.g., the mean value of thebottom quartile of the first plurality of calibrated methanemeasurements in plot 302). The range of the subset of calibrated methanemeasurement values can be representative of a predetermined percentilerange (e.g. bottom quartile, bottom quintile, etc.) of the firstplurality of calibrated methane values.

As described above, the various parameters (e.g., sensor measurementparameters, the global baseline reference, the threshold baseline valueand the previous baseline value, etc.) can be stored in a database(e.g., database 206). Prior to performing the calibration, thecontroller 204 can fetch one or more parameter values from the database206. Additionally or alternately, if the measurement baseline value isused in the calculation of offset parameter (e.g., when the measurementbaseline value is less than the threshold baseline value), the previousbaseline value can be set to the measurement baseline value.

This approach can have several advantages. For example, the averageglobal methane concentration has small variations (e.g., based ongeographic location), and can be a stable and reliable reference (e.g.,global baseline reference can be set to 1.88 PPMv). Automaticallycalibrating the drift in the measured baseline of the methane sensorusing the average global methane concentration in the atmosphere or asite specific known ambient methane concentration as a reference, andcalibrating the measurement data based on the offset between themeasured baseline of the sensor and the global baseline reference ofmethane concentration can be cheap and efficient. For example, noadditional sensors or data acquisition is needed. In someimplementations, the methane sensors deployed at industrial sites do nothave to be recalibrated (e.g. sent back to the factory forrecalibration) resulting in reduction of downtime and/or costs. In someimplementations, the computational cost for implementing thiscalibration can be small (e.g., calculation of offset may not becomputationally intensive). Moreover, some implementations of thisapproach can greatly improve the accuracy of the sensors (e.g., for lowmethane concentration such as below 10 parts per million by volume).

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the systems, devices, and methods disclosedherein. One or more examples of these embodiments are illustrated in theaccompanying drawings. Those skilled in the art will understand that thesystems, devices, and methods specifically described herein andillustrated in the accompanying drawings are non-limiting exemplaryembodiments and that the scope of the present invention is definedsolely by the claims. The features illustrated or described inconnection with one exemplary embodiment may be combined with thefeatures of other embodiments. Such modifications and variations areintended to be included within the scope of the present invention.Further, in the present disclosure, like-named components of theembodiments generally have similar features, and thus within aparticular embodiment each feature of each like-named component is notnecessarily fully elaborated upon.

The subject matter described herein can be implemented in digitalelectronic circuitry, or in computer software, firmware, or hardware,including the structural means disclosed in this specification andstructural equivalents thereof, or in combinations of them. The subjectmatter described herein can be implemented as one or more computerprogram products, such as one or more computer programs tangiblyembodied in an information carrier (e.g., in a machine-readable storagedevice), or embodied in a propagated signal, for execution by, or tocontrol the operation of, data processing apparatus (e.g., aprogrammable processor, a computer, or multiple computers). A computerprogram (also known as a program, software, software application, orcode) can be written in any form of programming language, includingcompiled or interpreted languages, and it can be deployed in any form,including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program does not necessarily correspond to a file. A programcan be stored in a portion of a file that holds other programs or data,in a single file dedicated to the program in question, or in multiplecoordinated files (e.g., files that store one or more modules,sub-programs, or portions of code). A computer program can be deployedto be executed on one computer or on multiple computers at one site ordistributed across multiple sites and interconnected by a communicationnetwork.

The processes and logic flows described in this specification, includingthe method steps of the subject matter described herein, can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions of the subject matter describedherein by operating on input data and generating output. The processesand logic flows can also be performed by, and apparatus of the subjectmatter described herein can be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processor of any kind of digital computer. Generally, aprocessor will receive instructions and data from a Read-Only Memory ora Random Access Memory or both. The essential elements of a computer area processor for executing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto-optical disks, or optical disks. Information carrierssuitable for embodying computer program instructions and data includeall forms of non-volatile memory, including by way of examplesemiconductor memory devices, (e.g., EPROM, EEPROM, and flash memorydevices); magnetic disks, (e.g., internal hard disks or removabledisks); magneto-optical disks; and optical disks (e.g., CD and DVDdisks). The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

To provide for interaction with a user, the subject matter describedherein can be implemented on a computer having a display device, e.g., aCRT (cathode ray tube) or LCD (liquid crystal display) monitor, fordisplaying information to the user and a keyboard and a pointing device,(e.g., a mouse or a trackball), by which the user can provide input tothe computer. Other kinds of devices can be used to provide forinteraction with a user as well. For example, feedback provided to theuser can be any form of sensory feedback, (e.g., visual feedback,auditory feedback, or tactile feedback), and input from the user can bereceived in any form, including acoustic, speech, or tactile input.

The techniques described herein can be implemented using one or moremodules. As used herein, the term “module” refers to computing software,firmware, hardware, and/or various combinations thereof. At a minimum,however, modules are not to be interpreted as software that is notimplemented on hardware, firmware, or recorded on a non-transitoryprocessor readable recordable storage medium (i.e., modules are notsoftware per se). Indeed “module” is to be interpreted to always includeat least some physical, non-transitory hardware such as a part of aprocessor or computer. Two different modules can share the same physicalhardware (e.g., two different modules can use the same processor andnetwork interface). The modules described herein can be combined,integrated, separated, and/or duplicated to support variousapplications. Also, a function described herein as being performed at aparticular module can be performed at one or more other modules and/orby one or more other devices instead of or in addition to the functionperformed at the particular module. Further, the modules can beimplemented across multiple devices and/or other components local orremote to one another. Additionally, the modules can be moved from onedevice and added to another device, and/or can be included in bothdevices.

The subject matter described herein can be implemented in a computingsystem that includes a back-end component (e.g., a data server), amiddleware component (e.g., an application server), or a front-endcomponent (e.g., a client computer having a graphical user interface ora web interface through which a user can interact with an implementationof the subject matter described herein), or any combination of suchback-end, middleware, and front-end components. The components of thesystem can be interconnected by any form or medium of digital datacommunication, e.g., a communication network. Examples of communicationnetworks include a local area network (“LAN”) and a wide area network(“WAN”), e.g., the Internet.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about” and “substantially,” are not to be limited tothe precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value. Here and throughout the specification andclaims, range limitations may be combined and/or interchanged, suchranges are identified and include all the sub-ranges contained thereinunless context or language indicates otherwise.

What is claimed is:
 1. A computer-implemented method comprising:receiving, by one or more processors from a methane detection systemcomprising a sensor, data characterizing methane detection by the sensorand sensor measurement parameters, wherein the data characterizingmethane detection comprises a plurality of methane measurements anddetection times associated with the plurality of methane measurements;wherein the sensor is located at an industrial site; determining, by theone or more processors, a first plurality of calibrated methanemeasurements by at least calibrating the plurality of methanemeasurements based on the sensor measurement parameters and one or moreof a humidity and a temperature associated with the sensor; calculating,by the one or more processors, an offset parameter based on a differencebetween a global baseline reference and one of a previous baseline valueand a measurement baseline value associated with the first plurality ofcalibrated methane measurements; and providing, by the one or moreprocessors, a second plurality of calibrated methane measurements by atleast subtracting the offset parameter from the first plurality ofcalibrated methane measurements.
 2. The computer-implemented method ofclaim 1, further comprising determining the measurement baseline valueby: selecting a subset of calibrated methane measurements from the firstplurality of calibrated methane measurements, wherein values of thesubset of calibrated methane measurements are below a predeterminedpercentile value, wherein the measurement baseline value is a mean ofthe subset of calibrated methane measurements.
 3. Thecomputer-implemented method of claim 2, wherein determining the offsetparameter comprises: determining that the measurement baseline value isless than a threshold baseline value; and determining the offsetparameter based on the difference between the measurement baseline valueand the global baseline reference.
 4. The computer-implemented methodaccording to claim 3, wherein the sensor measurement parameters, theglobal baseline reference, the threshold baseline value and the previousbaseline value are received from a database.
 5. The computer-implementedmethod of claim 4, further comprising updating the previous baselinevalue in the database by setting the previous baseline value to themeasurement baseline value.
 6. The computer-implemented method of claim2, wherein determining the offset parameter comprises: determining thatthe measurement baseline value is above a threshold baseline value; anddetermining the offset parameter based on the difference between theprevious baseline value and the global baseline reference.
 7. A systemcomprising: at least one data processor; memory coupled to the at leastone data processor, the memory storing instructions to cause the atleast one data processor to perform operations comprising: receiving,from a methane detection system comprising a sensor, data characterizingmethane detection by the sensor and sensor measurement parameters,wherein the data characterizing methane detection comprises a pluralityof methane measurements and detection times associated with theplurality of methane measurements; wherein the sensor is located at anindustrial site; determining a first plurality of calibrated methanemeasurements by at least calibrating the plurality of methanemeasurements based on the sensor measurement parameters and one or moreof a humidity and a temperature associated with the sensor; calculatingan offset parameter based on a difference between a global baselinereference and one of a previous baseline value and a measurementbaseline value associated with the first plurality of calibrated methanemeasurements; and providing a second plurality of calibrated methanemeasurements by at least subtracting the offset parameter from the firstplurality of calibrated methane measurements.
 8. The system of claim 7,wherein the operations further include determining the measurementbaseline value, the determining comprising: selecting a subset ofcalibrated methane measurements from the first plurality of calibratedmethane measurements, wherein values of the subset of calibrated methanemeasurements are below a predetermined percentile value, wherein themeasurement baseline value is a mean of the subset of calibrated methanemeasurements.
 9. The system of claim 8, wherein determining the offsetparameter comprises: determining that the measurement baseline value isless than a threshold baseline value; and determining the offsetparameter based on the difference between the measurement baseline valueand the global baseline reference.
 10. The system according to claim 9,wherein the sensor measurement parameters, the global baselinereference, the threshold baseline value, and the previous baseline valueare received from a database.
 11. The system of claim 10, wherein theoperations further comprising updating the previous baseline value inthe database by setting the previous baseline value to the measurementbaseline value.
 12. The system of claim 8, wherein determining theoffset parameter comprises: determining that the measurement baselinevalue is above a threshold baseline value; and determining the offsetparameter based on the difference between the previous baseline valueand the global baseline reference.
 13. A computer program productcomprising a non-transitory machine-readable medium storing instructionsthat, when executed by at least one programmable processor thatcomprises at least one physical core and a plurality of logical cores,cause the at least one programmable processor to perform operationscomprising: receiving, from a methane detection system comprising asensor, data characterizing methane detection by the sensor and sensormeasurement parameters, wherein the data characterizing methanedetection comprises a plurality of methane measurements and detectiontimes associated with the plurality of methane measurements; wherein thesensor is located at an industrial site; determining a first pluralityof calibrated methane measurements by at least calibrating the pluralityof methane measurements based on the sensor measurement parameters andone or more of a humidity and a temperature associated with the sensor;calculating an offset parameter based on a difference between a globalbaseline reference and one of a previous baseline value and ameasurement baseline value associated with the first plurality ofcalibrated methane measurements; and providing a second plurality ofcalibrated methane measurements by at least subtracting the offsetparameter from the first plurality of calibrated methane measurements.14. The computer program product of claim 13, wherein the operationsfurther comprising determining the measurement baseline value, thedetermining comprising: selecting a subset of calibrated methanemeasurements from the first plurality of calibrated methanemeasurements, wherein values of the subset of calibrated methanemeasurements are below a predetermined percentile value, wherein themeasurement baseline value is a mean of the subset of calibrated methanemeasurements.
 15. The computer program product of claim 14, whereindetermining the offset parameter comprises: determining that themeasurement baseline value is less than a threshold baseline value; anddetermining the offset parameter based on the difference between themeasurement baseline value and the global baseline reference.
 16. Thecomputer program product according to claim 15, wherein the sensormeasurement parameters, the global baseline reference, the thresholdbaseline value, and the previous baseline value are received from adatabase.
 17. The computer program product of claim 16, wherein theoperations further comprising updating the previous baseline value inthe database by setting the previous baseline value to the measurementbaseline value.
 18. The computer program product of claim 14, whereindetermining the offset parameter comprises: determining that themeasurement baseline value is above a threshold baseline value; anddetermining the offset parameter based on the difference between theprevious baseline value and the global baseline reference.